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Gastrointestinal > Introduction to GI tract and motility > Flashcards

Introduction to GI tract and motility Flashcards

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1
Q

What is the basic structure of the GI tract?

A

It is a series of hollow organs running from the mouth to the anus

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2
Q

What structures separate the hollow organs?

A

Sphincters

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3
Q

What is the function of the mouth and oropharynx?

A

The food is made into smaller pieces and lubricated. Fat and carbohydrate digestion starts and food is propelled to the oesophagus during swallowing

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4
Q

What is the function of the oesophagus?

A

Delivers food to the stomach

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5
Q

What is the function of the stomach?

A

Temporary food storage, continues carbohydrate and fat digestion, initiates protein digestion and regulates the delivery of chyme to the small intestine

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6
Q

What is chyme?

A

A pulpy acid fluid which passes from the stomach to the small intestine. It is made up of gastric juices and partly digested food

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7
Q

What is the function of the small intestine?

A

Principle site of digestion and absorption of nutrients

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8
Q

What is the function of the large intestine?

A

Reabsorbs fluids and electrolytes, stores faecal matter before regulated expulsion

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9
Q

What are the accessory structures of the digestive tract?

A

Salivary glands
Liver and gall bladder (hepatobiliary system)
Pancreas

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10
Q

What type of muscle drives motility of the GI tract?

A

Smooth muscle

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11
Q

What areas of the GI tract have skeletal muscle?

A

Mouth, pharynx, upper oesophagus and external anal sphincter

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12
Q

What are the three different mechanical activity of the GI tract?

A

Propulsive movements
Mixing movements
Tonic contractions

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13
Q

What controls secretions into the lumen of the digestive tract?

A

Hormonal and neural signals

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14
Q

What is the primary protective secretion throughout the length of the GI tract?

A

Mucus

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15
Q

What are the secretions required for?

A

Digestion and protection

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16
Q

What do the digestive secretions contain?

A

Water, electrolytes and organic compounds

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17
Q

What is digestion?

A

It is the biochemical breakdown of complex foodstuffs to smaller, absorbable units

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18
Q

What are carbohydrates broken down into?

A

Polysaccharides and disaccharides are converted to monosaccharides

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19
Q

What enzymes mediate the breakdown of carbohydrates?

A

Amylase and disaccharidases

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20
Q

What are proteins broken down into during digestion?

A

Amino acids, dipeptides and tripeptides

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21
Q

What enzymes mediate the breakdown of protein?

A

Proteases and dipeptidases

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22
Q

What are triglycerides (majority or fats) broken down into?

A

Monoglycerides and free fatty acids

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23
Q

What enzymes mediate the breakdown of triglyercides/

A

Lipases

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24
Q

What is absorption?

A

The transfer of absorbable products of digestion from the digestive tract to the blood or lymph

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25
What are the four layers of the digestive tract wall?
Mucosa Submucosa Muscularis externa Serosa
26
What is the mucosa comprised of?
``` Epithelial cells Exocrine cells Endocrine cells Lamina propia Muscularis mucosa ```
27
What does the submucosa contain?
Connective tissue Large blood and lymph vessels Nerve network - submucous plexus
28
What is the muscularis externa comprised of?
Circular muscle later Nerve network Longitudinial muscle layer
29
What does the serosa contain?
Connective tissue
30
Where foes the myenteric plexus lie?
Between the inner and outer layers or smooth muscle in the muscularis externa
31
What is the result of circular muscle contraction?
Lumen becomes narrower and longer
32
What is the result of longitudinal muscle contraction?
Intestine becomes shorter and fatter
33
What is the function of muscularis mucosae contraction?
Change in absorptive and secretory area of mucosa
34
What is the function of gap junctions?
Connect adjacent smooth muscle cells allowing the spread of electrical currents from cell to cell.
35
What is meant by a functional syncytium?
Hundreds of cells depolarise and contract at the same time
36
How is the sponatenous activity of the smooth muscle regulated?
Intrinsic (enteric) and extrinsic (automonic) nerves | Hormones
37
How is the electrical activity of the stomach, small intestine and large intestine described?
Slow waves - rhythmic patterns of membrane depolarisation and repolarisation that spread from cell to cell via gap junctions (variation in resting membrane potential)
38
What drives the slow waves?
Interstitial cells of Cajal (ICCs) - pacemaker cells
39
When does contraction occur?
When the slow wave amplitude is sufficient to trigger action potentials (reaches a threshold) and open voltage gated calcium channels
40
When does relaxation occur?
When the slow wave amplitude is sufficient to trigger action potentials (reaches a threshold) and open voltage gated postassium channels
41
How does slow wave electrical activity influence the force of contraction?
The longer the slow wave is above threshold the more channels are activated, meaning the greater the force of contraction
42
What do slow waves determine?
The basal electrical rhythm (BER) - which varies along the length of the GI tract
43
What factors influence whether the slow wave amplitude reaches the threshold?
Neuronal, hormonal and mechanical stimuli
44
What does the slow wave frequency set?
The maximum frequency at which the muscle can contract
45
What is the enteric nervous system?
The 'little brain of the gut' about 100million neurons A complete reflex circuit that can operate independently of the rest of the nervous system
46
Where is the enteric nervous system located?
In the GI tissue. Cell bodies are located in ganglia largely within the myenteric and submucous plexus
47
How are the ganglia connected?
Interganglionic fibre tracts
48
What is the enteric nervous system comprised of?
Sensory neurones Interneurones Effector neurones
49
What is the neurotransmitter for the parasympathetic system?
Acetlycholine
50
What is the excitatory influence of the parasympathetic branch of the enteric nervous system?
Increased gastric, pancreatic and small intestinal secretion Blood flow and muscle
51
What is the inhibitory influence of stimulation of the parasympathetic branch on the enteric nervous system?
Relaxation of some sphincters | Receptive relaxation of the stomach
52
What is the inhibitory influence of stimulation of the sympathtic nerves?
Decreased motility, secretion and blood flow
53
What are the three broad types of reflex that occur in the GI tract?
Local reflex Short reflex Long reflex
54
What is an example of a local reflex?
Peristalsis
55
What is an example of a short reflex?
Intestino-intestinal inhibitory reflex
56
What is an example of a long reflex?
Gastroileal reflex
57
What is peristalsis?
A wave of contraction that normally proceeds along the gut in an aboral direction (away form the mouth)
58
What triggers peristalsis?
Distension of the gut wall triggers interneurons that in turn trigger the motor neurons
59
What is the name of the segment before the food?
Propulsive segment
60
What is the name of the segment after the food?
Receiving segment
61
Describe the motility pattern segmentation?
Rhythmic contractions of the circular muscle layer that mix and divide luminal contents (area of relaxed muscle between the contracted circular muscle forms a sac)
62
What is name for segmentation in the large intestine?
Haustration
63
What are tonic contractions?
Sustained contractions found in the sphincters of the GI tract
64
How many sphincters are there in the GI tract?
6
65
How do sphincters work?
Act as a one way valve, maintain positive resting pressure relative to two adjacent structures
66
Describe the upper oesophageal sphincter?
Skeletal muscle Relaxes to allow swallowing Closes during inspiration
67
Describe the lower oesphageal sphincter
Relaxes to permit entry of food to the stomach | Closes to prevent reflux of gastric contents to the oesophagus
68
Describe the pyloric sphincter
Regulates gastric emptying and usually prevents duodenal gastric reflux
69
Describe the ileocecal sphincter
Regulates flow from the ileum to colon | Opens due to distension of the ileum, closes due to distension of proximal colon
70
What reflex regulates the internal and external sphincters?
Defecation relex
71
Which sphincters have skeletal muscle?
Upper oesophageal and external sphincter
72
What is the function of the lips?
Containment of food | Speech
73
What is the function of the teeth?
Mastication Food is broken down and mixed with saliva This stimulates taste buds which then increases salivary, gastric, pancreatic and bile secretion
74
What is the function of the palate?
Separates the mouth from the nasal passage, allows breathing and chewing simultaneously
75
What is the function of the uvula?
Helps seal off nasal passages during swallowing
76
What is the function of the tongue?
Guides food Important in speech and swallowing Major location of taste buds
77
What is the function of the pharynx?
Common pathways for the respiratory and digestive systems
78
What is deglutition?
The action/process of swallowing
79
What is swallowing?
The movement of food from the mouth to the stomach
80
What are the two stages of swallowing?
Oropharyngeal stage | Oesophageal stage
81
Describe the oropharyngeal stage
Mouth --> pharynx --> oesophagus (1 second) | Bolus formed --> food passes through pharynx into oesophagus
82
What happens to prevent food entering the nasal passages when swallowing?
Soft palate rises Tongue presses against the hard palate Uvula presses against the back of the throat
83
What happens to prevent food entering the trachea during swallowing?
Elevation of the larynx Tilting of the epiglottis Vocal cords close across the glottis The swallowing centre inhibits the resipiratory centre of the brain Pharyngeal muscles contract and force the bolus into oesphagus
84
What allows food into the oesophagus?
Opening of the upper oesophageal sphincter
85
Describe the oesophageal stage of swallowing
Oesophagus --> stomach (4-10 seconds)

Gastrointestinal (11 decks)

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